A lot of how a presentation looks, is determined by the Slide Master.
A Slide Master defines the default color palette, text styles, background, etc. Most presentations have one Slide Master, but some may have several.
In Microsoft PowerPoint, you can find the slide master by selecting the “View” section and then selecting “Slide Master”.
The Slide Master is the top slide in the thumbnail pane on the left side of the window. When you edit the Slide Master, all Slide Layouts that are based on that Slide Master will contain those changes.